The objective of this proposal is to investigate the role of calcium (Ca) ions in initiation and maintenance of ventricular fibrillation (VF). This study will provide insight to scientists and clinicians about the mechanism of VF that leads to sudden cardiac death (SCD). Understanding the mechanism of VF is essential for developing new therapies and nursing interventions to prevent and to decrease the incidence of SCD. The specific aims of this study are to: 1) measure intracellular membrane potential while recording the Ca transients; 2) determine the extent to which intracellular membrane potential and the Ca transients are correlated; 3) analyze the spatial distance between membrane potential and the Ca transients, and 4) develop an optical mapping system to permit simultaneous mapping of membrane potential and Ca transients. This study will use the right ventricle (RV) of nine swine during four modes of pacing including regular, incremental, irregular and rapid pacing resembling the rate of ventricular tachycardia and VF. Action potential duration restitution and Ca transients restitution will be constructed for each pacing modes. Pharmacological agents will be given, the effects will be documented and then the agents will be washed out and the effects will be documented again. At each stage of the study, electrical recording will be taken and optical mapping will be performed.